1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
An image forming apparatus that forms a toner image and transfers this to a recording medium, heats and pressurizes the recording medium onto which the toner image is transferred, and fixes the image to the recording medium, is widely used. There are cases wherein the image forming apparatus has a belt member (intermediate transfer belt, recording medium conveying belt, transfer belt, fixing belt, and pressurizing belt) that is steering-controlled by tilting a steering roller).
A belt steering control is generally a forced steering method in which a lateral position of a belt member is detected by a sensor, and the steering roller is forcibly tilted from the outside by a motor, based on the detection results thereof (Japanese Patent Laid-Open No. 9-169449). However, an autonomic steering method is also in use, wherein the steering roller is supported so as to be tiltable, and the steering roller can autonomously tilt and steer the belt member according to the lateral position of the belt member, without being driven externally (Japanese Patent Laid-Open No. 2001-146335 and PCT Japanese Translation Patent Publication No. 2001-520611).
The image forming apparatus disclosed in PCT Japanese Translation Patent Publication No. 2001-520611 has a pair of steering roller supporting members disposed tiltably on a frame member that rotatably supports a driving roller member. Both edges of the steering roller member are affixed rotatably to the pair of steering roller supporting members. Upon the belt member moving laterally, the rotating load momentum on the left and right of the steering roller member, of which a rotational axis of the steering roller supporting member is the center, is changed, and the steering roller member autonomously tilts and laterally moves the belt member.
In the image forming apparatus according to PCT Japanese Translation Patent Publication No. 2001-520611, a rotating shaft that tiltably supports a pair of steering roller supporting members bears the weight of the steering roller supporting members and the steering roller member by itself. Also, the rotating shaft of the steering roller supporting member bears by itself the force of the rotating load of the belt member, which occurs at the steering roller member, which urges the steering roller supporting member downstream in the rotating direction of the belt member. Therefore, the rotating shaft of the steering roller supporting member and the configuration that supports this rotating shaft on a frame member, have a considerable amount of rigidity.
Particularly, in a case wherein a belt cleaning device in which a cleaning blade abuts against a belt member supported on the steering roller is provided to a steering roller, the sliding load of the cleaning blade becomes the rotating load of the belt member. This load strongly urges the steering roller downstream in the rotating direction of the belt member, and applies a large bending force to the rotating shaft of the steering roller supporting members.